In the manufacture of communications cables, and, more particularly, in the manufacture of single strand lightguide cable, it has become the practice to connectorize the ends of the cable as a final step prior to storing or shipping.
In the case of single strand lightguide cable, which is most often used as patch cord or jumper cable for a main distributor frame, as an interface between optical and electrical apparatus such as, for example, regenerators and signal coders, or as connecting means between individual optical signal processing elements, such as are used in data links, varying lengths of cable are used. Thus, where both ends of the cable are connectorized, and the cable wound on a spool, the necessity of supplying a multiplicity of lengths requires an inordinate number of spools, since, preferably, only one complete connectorized cable is wound on a spool. Clearly, therefore, it is almost a necessity that the spool be comparatively inexpensive, durable, and, if possible, light in weight.
In the case of any connectorized cable, but perhaps most acutely in the case of single fiber lightguide cable, the connector itself must be protected from damage during handling and shipping. This arises from the nature of optical fiber cable connecting or splicing. A typical single fiber lightguide or cable connector is shown in "Interconnection for Lightguide Fibers" by T. L. Williford, Jr. et al, The Western Electric Engineer, Winter 1980, pp. 89-90. From that article it can be seen that the basic elements of the connector are a plastic conical plug at the end of the fiber with the fiber itself centered inside the plug and a biconical sleeve which accepts two plugs and is designed to produce alignment of the axes of the fiber ends. The biconical sleeve is a precisely molded part which includes two truncated conical cavities that control the end separation and axial alignment of the fiber end faces which are encapsulated within the plugs that are seated in the conical cavities of the sleeve. This axial alignment of the fiber end faces is critical, hence, it is essential that the connectors be protected after being mounted on the cable ends, especially during handling of the cable wound spool, so that the ability of the connectors to align the fibers is not impaired.
It is also important that there be as little microbending loss as possible in the vicinity of the connector. For example, should the lightguide cable exiting from the connector be bent at an extreme angle to the axis of the connector, microbending losses exceeding an acceptable amount could be imparted to the cable. Wher it is desired or necessary to make measurements on the cable wound on the spool, such losses could seriously hamper the achievement of any meaningful results. In addition, too sharp a bend could result in permanent damage to the cable.
In the interests of efficiency and economy, a spool that can be easily assembled, used in the manufacturing process, handled, and shipped to the customer, and then broken down and destroyed or returned to the cable manufacturer is highly desirable. Examples of spools which are separable into two or more components are shown in U.S. Pat. No. 3,358,943 of E. Pelson and U.S. Pat. No. 3,635,421 of D. E. Boland et al. For reasons which will be apparent hereinafter, such spools as are shown in these patents would not be satisfactory for supporting a wound single fiber connectorized lightguide cable, even though they do possess the desirable feature of separability.